Define an XML element that must be empty and has no attributes

Question

I needed to define an XML element that has no sub-elements or any content at all, and has no attributes.

This is what I am doing:

<xs:element name="myEmptyElement" type="_Empty"/> <xs:complexType name="_Empty"> </xs:complexType> 

This appears to work fine, but I have to wonder if there is a way to do this without having to declare a complex type. Also, if there is anything wrong with what I have, please let me know.

Anticipating that someone might be curious why I would need such an element: It is for a SOAP operation that does not require any parameter values.

Answer 1

(1) You could avoid defining a named xs:complexType:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">   <xs:element name="myEmptyElement">     <xs:complexType/>   </xs:element> </xs:schema> 

(2) You could use a xs:simpleType instead of a xs:complexType:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">   <xs:element name="myEmptyElement">     <xs:simpleType>       <xs:restriction base="xs:string">         <xs:maxLength value="0"/>       </xs:restriction>     </xs:simpleType>   </xs:element> </xs:schema> 

(3) You could use fixed="" ^{_{[credit: @Nemo]}}:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">   <xs:element name="myEmptyElement" type="xs:string" fixed=""/> </xs:schema> 

(4) But note that if you avoid saying anything about the content model:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">   <xs:element name="myEmptyElement"/> </xs:schema> 

You'll be allowing any attributes on and any content in myEmptyElement.

Answer 2

Another example could be:

<xs:complexType name="empty">     <xs:sequence/> </xs:complexType> <xs:element name="myEmptyElement" type="empty> 

or

<xs:element name="myEmptyElement">     <xs:simpleType>         <xs:restriction base="xs:string">             <xs:enumeration value=""/>         </xs:restriction>     </xs:simpleType> </xs:element> 

or

<xs:element name="myEmptyElement">     <xs:complexType>         <xs:complexContent>             <xs:restriction base="xs:anyType"/>         </xs:complexContent>     </xs:complexType> </xs:element>